Traditionally, copier, in the office equipment context, refers to light lens xerographic copiers in which paper originals are in fact photographed. The images are focused on an area of a photoreceptor, which is subsequently developed with toner. The developed image on the photoreceptor is then transferred to a copy sheet which in turn is used to create a permanent copy of the original.
In recent years, there has been made available what is known as digital copiers. With respect to the most basic functions, a digital copier performs the same functions as a light lens copier, except that the original image to be copied is not directly focused on a photoreceptor. Instead, with a digital copier, the original image is scanned by a device generally known as a raster input scanner (RIS) which is typically in the form of a linear array of small photosensors.
The original image is focused on the photosensors in the RIS. The RIS converts the various light and dark areas of the original image to a set of digital signals. These digital signals are temporarily retained in a memory and then eventually used to operate a digital printing apparatus when it is desired to print copies of the original or a display screen when it is desired to display the image; i.e., the image is scanned and converted to electrical signals so that the image can be used for other reproduction or storage purposes. The digital signals may also be sent directly to the printing device or display device without being stored in a memory. The digital printing apparatus can be any known type of printing system responsive to digital data, such as a modulating scanning laser which discharges image portions of a photoreceptor, or an ink jet printhead.
With the migration of the copying and scanning systems to a digital base system, the systems faced different problems than from the light lens or analog copying systems. More specifically, in a digital reprographic system, the scanning system needs to locate the actual location of the document so that any desired image processing routines can be applied to the correct pixels of image data. Moreover, a digital reprographic system should determine the background type of the original to ensure optimal rendering.
In describing the present invention, the terms pixel will be utilized. This term may refer to an electrical (or optical, if fiber optics are used) signal which represent the physically measurable optical properties at a physically definable area on a receiving medium. The receiving medium can be any tangible document, photoreceptor, or marking material transfer medium Moreover, the term pixel may refer to an electrical (or optical, if fiber optics are used) signal which represent the physically measurable optical properties at a physically definable area on a display medium. A plurality of the physically definable areas for both situations represent the physically measurable optical properties of the entire physical image to be rendered by either a material marking device, electrical or magnetic marking device, or optical display device.
Lastly, the term pixel may refer to an electrical (or optical, if fiber optics are used) signal which represents physical optical property data generated from a single photosensor cell when scanning a physical image so as to convert the physical optical properties of the physical image to an electronic or electrical representation. In other words, in this situation, a pixel is an electrical (or optical) representation of the physical optical properties of a physical image measured at a physically definable area on an optical sensor.
In a digital scanning system, it is desirable to perform image processing routines which will optimize the reproduction of the image of the document. These routines could include improving the contrast between the desired image and the document's background. In other words, it is sometimes desirable to remove the background of a document and replace this image data with a reference white value so that the desired image becomes sharper and more discernible in the reproduced document. This replacement of the background with a reference value is only effective if the background is uniform. If the background is not uniform, the desirable image data may be lost with such a global replacement.
Thus, it is important in a digital scanning system to determine the background value of the document being scanned; i.e., whether the document has a white or dark background; and to determine if the background of the scanned document is uniform or not. This determination of the background value and its uniformity for a document is particularly important in an engineering document scanning system.
In an engineering document scanning system, the input document can have a wide range of backgrounds with some documents having uniform backgrounds and others having non-uniform backgrounds. For example, engineering scanners are used to scan large format engineering documents such as CAD drawings, diablo, vellum, and sepia, etc., and to convert these scanned documents to binary bitmap image for printing. One of the most challenging tasks for an engineering scanner is to have the ability to scan these diverse originals with only one trial and produce a good quality binary image for printing. The original ranges from normal white background to dark sepia with the background level below 10 digital count for an 8-bit scanner. The diversity in originals makes it very difficult to manually determine a correct darkness setting to reproduce the original with a binary printer. Conventionally, the operator uses trial-and-error methods to find the correct threshold.
Such a trail and error process consumes the time and energy of the user and adversely impacts productivity. Moreover, this conventional manual method produces wasted copies since a user cannot always input the correct contrast value the first time. Thus, it would be desirable to have an automatic background detection system to determine the document's background value and whether the background is uniform when the document is being scanned.
The present invention demonstrates an automatic and simple low cost system and method to optimally render an engineering document. More specifically, the present invention proposes a method and system for providing automatic detection of the background value and background type of a document wherein the present invention utilizes a ratio of the white peak to the half power width of the histogram white peak to determine the background type of the document. By utilizing this ratio, the uniformity of the document's background can be verified while significantly reducing false determinations of uniformity. Once the background value is determined and its uniformity is verified, the present invention can adjust the A/D voltage reference and the tone reproduction curve (TRC) to effectively compensate for the background difference between different originals and to make it possible to render difficult images with only one trial. This method can improve the productivity and reduce the cost associated with wasted bad copies and operator's time.